Plasma contains a variety of proteins which have specific biologic functions, some known and well defined for a given protein, some still to be determined. Any plasma protein deficiency occurring either as a congenital disease or as an acquired state associated with a pathologic condition may indicate the need for replacement therapy. Because of technologic advances in the collection, storage and fractionation of plasma, a single unit of blood can now supply many concentrated, purified proteins for different therapeutic uses. For example, plasma was formerly the mainstay of hemophilia A and hemophilia B therapy; it is now used only when no other source of Factor VIII or Factor IX (the respective deficient factors) is available. It is currently considered poor practice to use unfractionated materials except in an emergency, because of the difficulty of achieving adequate and sustained therapeutic levels of the deficient materials without inducing circulatory overload. With the introduction of new techniques for protein purification and the recognition of congenital or acquired pathological states associated with specific protein deficiency, a number of plasma derivatives or concentrated fractions have been made available for the treatment of specific plasma protein deficiencies.
Prothrombin complex concentrates are clinically employed in current replacement therapy for patients with deficiencies of the vitamin K-dependent clotting Factors II, VII, IX and X. These concentrates, also referred to as Factor IX concentrates, Factor IX complex concentrates, and PPSB (prothrombin, proconvetin, Stuart factor, and antihemophilic B factor), have demonstrated efficacy in the treatment of hemophilia B (Christmas disease) by alleviating hemorrhagic episodes and preventing post-surgical complications. The efficacy of these Factor IX concentrates for replacement therapy in deficiencies of prothrombin (Factor II), Factor VII, and Factor X is also generally accepted, although the incidence of congenital deficiency of these factors is much rarer, and fewer data are available. Factor IX complex concentrates have, however, been implicated as a cause of thromboembolic complications and disseminated intravascular coagulation (DIC), particularly in patients with acquired deficiencies of the vitamin K-dependent clotting factors, especially those with liver disease. In patients with hemophilia B, thrombohemorrhagic complications occasionally result from infusions of conventional Factor IX complex concentrates. The reaction to these concentrates may be quite severe, with manifestations including superficial vein thrombosis, deep vein thrombosis, pulmonary embolism, and myocardial infarction. Fatalities believed to be directly attributable to commercial Factor IX complex concentrates have been documented.
While attempts have been made to devise reliable in vitro methods for the prediction of potential thrombogenicity in Factor IX complex concentrates and to identify the agent or agents present in these concentrates responsible for inducing thromboembolic complications, the results have been inconclusive. Experiments with animal models have demonstrated a correlation between non-activated partial thromboplastin time (NAPTT) and in vivo assays for thrombogenicity; the thrombingeneration test (TGt50) also correlates with in vivo test results. Using these and other in vitro tests, in conjunction with in vivo assays in animal models, researchers have suggested various causes of the thrombogenic activity associated with Factor IX complex concentrates prepared by standard methods, including Factors Xa, IXa, VIIa, and factors of the contact phase; Factor XIIa activation of prekallikrein; and high levels of zymogens extraneous to the deficient factor in the concentrates. Also considered as a possible factor in the adverse activity of the concentrates is Factor VIII bypassing activity. Unfortunately, available in vitro tests, including NAPPT and TGt50 are not reliably predictive of clinical thrombogenicity, and in vivo animal studies have proved inconclusive for various reasons. The lack of reliable in vitro tests and the impracticality of extensive in vivo testing has seriously hampered research attempts to isolate the causative agent or agents of the documented thromboembolic complications. As succinctly stated by Coan, et at. in "Properties of Commercial Factor IX Concentrates" (Ann. N.Y. Acad. Sci., 731-746; 734, 789, 1981), "Various investigators have proposed at one time or another than any of the activated coagulation factors are the cause of thrombogenicity. These include Factors VIIa, IXa, Xa, and XIa. There are no consistent results. The actual thrombogenic agent may be none, one, several or all of the above . . . . Results [of extended investigations] suggest that some as yet unidentified component of the Factor IX preparation may well be involved in the occurrence of thrombogenic reactions independent of the state or concentration of the major vitamin K-dependent factors."
It is accordingly highly desirable to provide concentrated plasma protein fractions useful for replacement therapy in congenital or acquired deficiencies of vitamin K-dependent clotting factors but which have little or no thrombogenic potential. From a practical standpoint, it is particularly desirable to provide a Factor IX concentrate devoid of thrombogenic agents but retaining clinical activity for the control of hemorrhage in hemophilia B patients, owing to the relatively more common incidence of this deficiency disease.